Hi, Melissa! You're definitely right. Soy paint is just fine for a hamster, if yours does ingest a bit it's fine. I found my white soy paints for my guinea pigs at Amazon. If you're curious, the brand is Delta. If you order from Amazon.com a lot, I'd reccomend getting Prime to get free shipping on the item. As for a DIY paint, I'm not sure about white. I'll let you know if I find anything else!

you can make homemade, hamster-safe paint out of fruit, vegetables and water.
Basically, you select a hamster-safe fruit or vegetable the color that you want your "paint" to be. (For example, if you want red "paint", you can use strawberries.) First, chop up the fruit or vegetable you're using. If the fruit or vegetable is hard (like carrot), put it in the blender with some water (the more water you put, the paler yur color will be) until it's completely demolished. You can also use the blender for soft fruitor vegetables, like lettuce. For soft fruits, you can try boiling it in water. Once you finish demolishing them, hopefully you'll have a bunch of juice left over from the fruit or vegetable. Put the pulp/juice through a strainer over a bowl, to get the juice separated from the pulp. (Don't throw away the pulp, though! It'll make a very nice hamster treat!) it totally edible and safe.